Abstract: An optical branched waveguide and an optical waveguide circuit which are easily fabricated, have a small size, and are low in cost. A linear first optical waveguide and second optical waveguide are crossed at a predetermined angle with respect to the substrate, a groove forming a predetermined angle relative to the optical waveguides and having a depth set to not less than the depth of the first and second optical waveguides is formed so as to include the intersecting region of the first optical waveguide and the second optical waveguide, and an optical element having a partial reflection and partial transmission function passing part of an incident light guided through the first optical waveguide therethrough and guiding this to the first optical waveguide and, at the same time, reflecting part of the incident light and guiding the same to the second optical waveguide is inserted into the groove so as to include the intersecting region of the first optical waveguide and the second optical waveguide.

Abstract: A PTC composition comprising at least one polymer, from 5% to 45% by volume of electrically conductive or semiconductive particles having a room temperature electric conductivity of at least 10.sup.2 [s/m] dispersed in said polymer, and from 0.2% to 20% by volume of thermally conductive particles having a room temperature electric conductivity of no more than 10.sup.-3 [s/m] and a thermal conductivity of at least 20 [w/m.multidot.k] dispersed in said polymer. A PTC device using such a PTC composition has a high ratio of peak resistance to room temperature resistance, and exhibits high safety.

Abstract: A cesium beam tube for use as a frequency standard, wherein the beam path from the cesium beam source unit to the detector is hermetically sealed.This cesium beam tube includes a rigid high frequency transition part composed of a metallic block which is used as the basic support of the tube. A first state selection magnet part and the cesium beam generator are coaxially coupled to the one end of the rigid cavity, while the second state selection magnet part and detector are coaxially connected to the other end of the rigid cavity. The rigid cavity, first and second magnet poles, cesium beam generator and the detector form the vacuum envelope by themselves, and the permanent magnets and other related parts are not in a vacuum.